Method of reclaiming stainless steel scrap



,5!) higher grade,

Patented Sept. 29 1931 LEwrs B. Lmnrmu'rrr; or m Yomr, n. Y,

- METHOD or mammal srAmEEss s'rEEI. sonar No Drawing.

The invention relates to a-method of producing high grade stainless steel from scrap of the alloyand also from the scrap of the lower grade stainless steel and has for its '6' object to simplify and expedite the operations necessary to this end.

So-called stainless steels or alloys of iron and chromium, in some instances containing nickel, are of two recognized grades, one

containing carbon below ,07% and the other having a carbon content from .07 to .16% carbon. The high grade stainless steel usually contains from 8% to 9% ofnickel and 16.5% to 19% of chromium. Phe steel containing the lower percentage of carbon is desirable for most purposes and is more diflicult to make.

In the manufacture of articles from so-.

called stainless steels, there is a considerable element of scrap and heretofore attempts to utilize this scrap, especially in producing the high grade stainless steels low in carbon, have generally failed because the remelting of the scrap causes an increase in the percentage of l carbon, which cannot be reduced by ordmary methods without impairing the character and quality of the final alloy or stainless steel.

It has been possible to remelt the scrap in an electric furnace of the are or of the induction type, with an increase in carbon, which permits it to be used for the higher carbon grades of stainless steel, but which are less desirable in the trade. Upon re- 5 melting of the scrap resulting from the high carbon grade of stainless steel, the increasein. the carbon content is so great as to render the steel practically valueless. The aforesaid conditions materially increase the cost of stainless steels in both these grades, because of the scrap wastage, which could not herecovered or restore the present invention is desi ed to utilize scrap of either grade of staind steel which has been fabricated with too high a carbon content for practical use and the method may be successfully and economically applied to the conversion ofthese various types-of steel into stainless steel of the to wit, that containing the .the chromium in the slag is adde to commercial form, but

ess steel or of Application tiled July 30, 1980. Serial No. 471,898.

lower percentage of carbon not in excess of In carrying out the process, the sore is melted in an electric furnace and the mo ten metal tapped into a ladle and from 1% to 5 2% of an exothermic reducing agent added to the melt, which reducing agent ma be silicon, but is preferably comminute aluminum. The molten mass is then transferred to a bottom blown Bessemer converter, prefera ably with a neutral lining, which may be chrome ore, although, if desired, a converter with a basic lining, such as magnesite, ma be used. The converter, with its charge, is en blown for a period of time suflicient to reduce a the carbon content below .07 and to oxidize approximately 8% of a chromium, which latter goes into the slag. As a practical example, the blowing of three tons of the molten metal, as described, would require 4 min- 1 utes to effect the necessary reduction of the carbon and the oxidation of the chromium to'the percentages indicated. After the blow has been completed and the converter is turned down, sllicon in an amount sufiicient to reduce and recover approximatel 2% of to the blow. This will leave an additional amount of 6% of chromium to be incorporated with the molten metal to produce the stainless steel. It has been found possible with the temperatures developed inthe converter and immediately after the blow has been completed, to add 3% of chromium in the form of carbon free ferro-chromium, which will be as readil taken up by the melt. This leaves 1 3% o chromium to be added to produce the desired high grade stainless steel and this is supplied to the molten bath in the form of carbon free ferro-chromium reduced in a separate vessel by alumino-thermic reaction or by the similar reduction of pure metallic chromium, a sufficientquantity of the alumino-thermic metal being added to the reviously prepared melt to supply the additionas .al 3% of chromium.

What I claim is:

1. The method of reclaiming stainless steel scrap, which comprises melting the scrap in an electric furnace, tapping the melt into a 109 ladle, adding thereto from 1% to 2% of an exothermic reducing agent, transferring the molten mass to a Bessemer converter, blowing the same until the carbon content is re 5 duced below .07 and sapproxima" teli 8% of the chromium is oxidize adding to t e molten blown product farm-chromium to supflyapproximately 3% of chromium melting erro-chromium by the elumino-t ermic reacm tion in a separate crucible, and adding an the carbon content is reduced alumino-thermic reaction in a separate crucible, and adding an amount of the melt to the aforesaid blown product to bring the chromium content to t e desired total percentage of the alloy. 1

3. The method of reclaiming stainless steel scrap, which comprises melting the scrap in an electric furnace, tapping the melt into a ladle, adding thereto from 1% to 2% of an exothermic reducing agent, transferring the molten mass to a Bessemer converter, blowing the same until the carbon content is reduced below .07% and approximately 8% of t the chromium. is oxidized, adding to the molten blown product silicon to effect reduction of approximately 2% of the chromium in the slag and further adding thereto ferro-chromium to supply approximately 3% of chromium, melting ferro-chromium by the alumino-thermic reaction in a se arate crucible,

and adding an'amount of e melt to the aforesaid blown product to bring the chr0- mium content to the desired total percentage of the alloy.

' In testimony whereof I alfix my signature.

B. LINDEMUTH. 

